PackageManagerService: fix NPE while renaming foreign dex markers.

The User passed in to scan*LI is null during the initial boot scan
and maybeRenameForeignDexMarkers wasn't expecting it. We attempt to
rename markers for all users if that happens.

bug: 29167406
Change-Id: I892dcc542e75d62d72c062b8ce5506ef85df5fc2